This invention generally relates to tools for installing blind bolts, and more specifically relates to a blind bolt installation tool which includes springs having different ratings to overcome certain problems experienced in the prior art as discussed hereinafter.
FIGS. 1-10 illustrate two different pulling heads 10a (FIGS. 1-5) and 10b (FIGS. 6-10) for installing blind bolts such as that which is shown in the drawings (see also U.S. Pat. Nos. 4,432,679 and 4,844,673 which are hereby incorporated herein by reference in their entirety). As shown, the pulling heads 10a, 10b may be configured to work with blind bolts which include a mandrel 28a, 28b, a shift washer 62 and a sleeve 63, wherein the mandrel is pulled to install the fastener 12a, 12b, and the mandrel 28a, 28b breaks off during installation.
In general, concerning the disposition of jaws before a fastener is inserted, pulling heads can be classified into two categories: “open jaw” and “closed jaw” designs. In both designs, a set of jaws grip the mandrel of the fastener. In an open jaw design, the jaws are normally open, and must be closed onto the mandrel. In contrast, in a closed jaw design, the jaws are normally too close together to insert a mandrel between them. Therefore, the jaws must be opened in order to insert the mandrel.
FIG. 1 illustrates a pulling head 10a having a closed jaw design, while FIG. 6 illustrates a pulling head having 10b an open jaw design. Each pulling head is configured to be threadably engaged with an installation tool, which for clarity, is omitted from the drawings. When an installation tool is engaged with the pulling head 10a or 10b, and the installation tool is actuated, the installation tool operates the pulling head to install a fastener.
As shown in FIG. 1, the closed jaw pulling head 10a includes a set of jaws 14a (a typical set having two or three jaws) about the longitudinal axis 16 of the pulling head. Each jaw 14a of the set includes an angled or conical portion 18 on an outer surface 20 and a serrated portion 22 on an inner surface 24, where the serrated portion 22 is configured to grippingly engage corresponding serrations 26 provided on the mandrel 28 of a fastener or blind bolt 12a. 
The jaws 14a are disposed in a taper 30 provided in a collet 32a. When the jaws 14a are in the forward-most position as illustrated in FIG. 1, the internal diameter 34 defined by the jaws 14a is generally smaller than the diameter 36 of the mandrel 28a of the fastener 12a to be inserted in the jaws 14a. The fastener 12a is a conventional blind bolt design, generally as shown in the abovementioned U.S. Pat. Nos. 4,432,679 and 4,844,673 and numerous other prior art patents. Hence, the jaws 14a are said to be “closed.” A threaded portion 38 is provided in the collet 32a for engagement with a head piston of the installation tool. The collet 32a is generally cylindrical and includes a main internal bore 40. The jaws 14a, a jaw follower 42a, and a follower spring 44a are disposed in the collet 32a. The jaw follower 42a holds the jaws 14a generally in position. The jaw follower 42a is also generally cylindrical and includes a longitudinal throughbore 46 which is configured to receive a broken stem or mandrel 28a of the blind bolt or fastener 12a. 
The jaw follower 42a is subject to a spring load viz-a-viz the follower spring 44a. One end 48 of the follower spring 44a contacts a shoulder 50 on an outer surface 52 of the jaw follower 42a, while the other end 52 of the follower spring 44 contacts the installation tool when the installation tool is engaged with the pulling head 10a. The follower spring 44a effectively acts as a shock absorber when the mandrel 28a of the fastener 12a breaks during installation, keeping the jaw follower 42a from accelerating rapidly backwards and impacting other components. The collet 32a is disposed in a sleeve 54a, and is moveable relative thereto. A threaded aperture 56 is provided at an end 58 of the sleeve 54a, and a nosepiece 60a is threadably engaged in the threaded aperture 56.
In operation, as the mandrel 28a of a fastener 12a is inserted into the nosepiece 60a as shown in FIG. 2, the mandrel 28a opens the jaws 14a against the spring load (provided by spring 44a). The mandrel 28a is pushed into the nosepiece 60a until a shift washer 62 of the fastener 12a bottoms on or contacts the nosepiece 60a as shown in FIG. 3. Because the jaws 14a sit in a taper 30, the jaws 14a have to move back as they expand, until their serrations 22 are aligned with the serrations 26 of the mandrel 28a. As the jaws 14a open, the serrations 26 on the mandrel 28a rub against the serrations 22 of the jaws 14a, causing wear. To minimize operator effect, and the possibility of fastener disassembly between the sleeve 54a and the mandrel 28a, the follower spring 44a is preferably configured to have a relatively small spring rate.
As shown in FIG. 4, when the tool is actuated (i.e., the trigger of the tool is depressed), the collet 32a, which is threadably attached to the head piston of the installation tool, moves back under load. The travel of the head piston (not shown) is known as the “stroke” of the tool, said “stroke” being identified with arrow 62 in FIG. 4. The taper 30 of the collet 32a transfers the pulling force of the tool to the jaws 14a, which grip the mandrel 28a. The fastener 12a is installed as the mandrel 28a moves relative to the sleeve 63 of fastener 12a, to deform the sleeve 63 and set the locking collar as is conventional in the art, and as shown in the previously-mentioned patents. The pulling force continues until the mandrel 28a fractures or breaks at the break notch, thus completing the installation. Because the follower spring 44a must also act as a shock absorber, the break load of the fastener must be relatively small, so that the spring 44a can absorb the kinetic energy of the installation without taking too much of a permanent “set.” When the mandrel 28a breaks off, the mandrel 28a is still held by the jaws 14a. 
When the installation tool's trigger is released, the head piston and collet 32a return to their home position as shown in FIG. 5. As shown, the broken mandrel 28a is still held in the jaws 14a under a spring load. When the next fastener is inserted, its mandrel will push the broken mandrel of the previously installed fastener through the jaws 14a, causing more wear.
FIG. 6 illustrates an open jaw pulling head 10b. The design is similar to the closed jaw pulling head in that the design includes a sleeve 54b, a collet 32b, jaws 14b, a jaw follower 42b, a follower spring 44b, and a nosepiece 60b. However, in an open jaw design, the jaws 14b are forced open when in their forward-most or home position such that the inner shape formed by the jaws 14b is larger than the diameter of the fastener to be inserted. This is usually accomplished by a rear protrusion 64 of the nosepiece 60b, which protrudes into the collet 32b, being configured to open the jaws 14b when the pulling head is in its “home” position. Therefore, the jaws 14b are open before the mandrel or stem 28b of the fastener 12b is inserted, allowing the mandrel 28b to be inserted with no resistance, and also removed, if necessary.
FIG. 7 illustrates a mandrel 28b placed in the pulling head 10b. There is no resistance involved in placing the mandrel 28b in this position because the inner diameter 70 of each of the jaws 14b is larger than the diameter of the mandrel 28b, so the fastener 12b could also be inserted and retained by a vacuum force. At this point, the jaws 14b are forced open by the rear protruding portion 64 of the nosepiece 60b. The jaws 14b are forced back by this protrusion 64 and, therefore, are forced open and outward against the taper 72 of the collet 32b by the spring load. At this point, the fastener 12b could be removed from the pulling head 10b, because the jaws 14b are not gripping the mandrel 28b. 
When the rivet tool is activated, the collet 32b begins moving back, away from the nosepiece 60b, as shown in FIG. 8. The jaws 14b begin to close in the taper 72 of the collet 32b as the protrusion 64 of the nosepiece 60b into the collet 32b diminishes. As the collet 32b pulls away from the rear protrusion 64 of the nosepiece 60b, the jaw set is pushed forward by the spring load and closes on the stem 28b. The smaller the stem 28b, the more stroke it takes for the jaws 14b to make contact. Subsequently, the mandrel 28b is pulled until the fastener 12b is installed.
As illustrated in FIG. 9, the mandrel 28b breaks and the collet 32b travels to its extreme position as the tool completes its stroke. More stroke is required to install a fastener using an open jaw pulling head design than is required by a closed jaw design. After the mandrel 28b breaks, the mandrel 28b is still held by the jaws 14b. 
As shown in FIG. 10, as the collet 32b returns to its “home” position at the end of the tool cycle, the nosepiece 60b again contacts and opens the jaws 14b, allowing the mandrel 28b to be released. The broken stem 28b is free to move under the force of gravity, or to be extracted by a vacuum force. In either case, the jaws 14b experience no wear from the extraction or by the insertion of the next fastener.
Because the mandrel 28b does not have to force open the jaws 14b upon insertion (see FIG. 7), the follower spring 44b can be stronger than in the closed jaw design. This spring 44b could absorb more kinetic energy, so the break load of the fastener used could also be higher than in the closed jaw design. However, the mandrel 28b of a fastener used in the open jaw design must be long enough to extend beyond the longer nosepiece 60b, far enough so that the jaws 14b can grip it. Also, the stroke of the tool that is used while the jaws 14b close on the mandrel 28b is wasted.
Typically, closed jaw designs such as that which is shown in FIGS. 1-5 are used to install low-break load fasteners. Closed jaw designs typically employ an internal spring (i.e., part number 44a as discussed above and identified in FIGS. 1-5) which has a relatively low spring rate. The arrangement makes the installation of different size diameters with relatively short stem fasteners possible. In contrast, open jaw designs such as that which is shown in FIGS. 6-10 are typically used to install a single size diameter of high-break load fastener. Open jaw designs typically employ an internal spring (i.e., part number 44b as discussed above and identified in FIGS. 1-5) which has a relatively high spring rate. The arrangement makes the installation of different size diameters very difficult, and makes the installation of fasteners with very short stems impossible.